1. Field of the Invention
The invention relates to a pump for fluids of the type having a pair of identical pump units which are connected to a motor driven shaft via a drive unit that has a drive element, and a power transmission element, and having a support member to which casings of the pump units are fixed.
2. Description of Related Art
The known pump from which the invention originates (U.S. Pat. No. 3,697,197) is an ice cream pump that serves to pump liquid and air simultaneously in respective cylinders. The pressures applied in the intended use environment are low pressures from slightly above atmospheric pressure up to a maximum of 2 bar.
The noted pump is a self-contained, double-acting pump having a pair of piston cylinder pump units that are driven by a motor, such as an electric motor. The double-acting pump is connected by a flanged joint to the electric motor or the motor frame. Each pump unit, itself, is of a very practical, simple, and economical modular design. All parts of the pump are held together by a support which is made as a U-shaped frame and which is flange mounted, by a plate-like crosspiece onto a bearing bracket of the motor. Each pump unit is mounted on a respective plate-like side leg of the U-shape of the frame, with the pump units placed facing each other with mirror-image symmetry. The casings of the pump units are configured to provide a pipe-shaped part with open inlet and outlet ends for holding a suction valve or a pressure valve and a cylindrical part which projects at a right angle away from the pipe-shaped part to provide a cylinder working space for guiding the pump piston. Valve bodies of the suction valve and pressure valve are set in the end openings of the casings after which the end openings are closed with end caps. A complete bracing of all parts occurs by setting the pump units on the support.
The opening in the casings for the piston rods or the pump pistons of the pump units are placed on the long sides of the casings and are axially aligned with one another. The pump pistons are connected with a yoke-like power transmission element having a central channel section which receives a cam roller of a crank-like drive element of the drive unit. The drive element is seated on the front end of the drive shaft of the motor with the axis of rotation of the cam roller eccentric to the longitudinal axis of the drive shaft. Optionally, a suitable permanent lubrication can be provided here; although the open arrangement of this construction automatically yields good cooling, especially in the area of the drive element of the drive unit and the power transmission element.
The support of the known pump exhibits an opening for the drive shaft to pass through so that the support can be flange mounted directly onto the bearing bracket of the motor, and the power transmission element and drive element received in a space between the sides of the U-shaped frame. When an electric motor is used, for example, the bearing on the output side of the motor shaft, specifically the armature bearing on the output side of the electric motor, can be used as a bearing for the drive shaft.
The attachment of both pump units onto the sides of the U-shaped support frame occurs from the outer side of the frame, and the perpendicularly projecting part of the casing that forms the work space is inserted through a suitably shaped opening in each side leg of the U-shaped frame. Threaded rods project from the sides of the support, and the casings can be slid onto these rods and held in place with the help of threaded knobs. A flange-like edge surrounds the frame opening provided for passage of the part of the casing which provides the piston work space and acts together with a ring-like flange on the casing of each pump unit itself so that the pump units can simultaneously be aligned with one another and adjusted when the units are fixed in place.
The known pump described above is not suitable for higher pressures for many reasons. On the one hand, the necessity of connecting the two pump units of the pump with one another by hose lines in a relatively complicated operation is problematical for high pressure applications since weak points result each time from the hose lines. In any case, such hose lines are decidedly expensive for high pressures above 20 bar. Further, at high pressures, correspondingly high drive power is, naturally, needed which, of course, requires correspondingly considerably increased material strengths. That also immediately results in considerably higher prices. As a result, a pump of the kind discussed that is reinforced so that it is suitable for pressures above 20 bar becomes as expensive or more expensive than high pressure pumps of the type specially developed for these pressure ranges and designed differently.
Conventionally, high pressure pumps, in other words pumps for a pressure range between 20 and 100 bar, especially a pressure range between 40 and 80 bar, are so expensive primarily because it has been generally accepted that a large and heavy, all encompassing metal casing cannot be dispensed with. This casing is normally flanged with the motor mount of a drive motor by a further supporting structure. At the same time, a drive shaft of the high pressure pump doubly supported in the casing itself is connected by a flanged joint located between the casing of the drive motor and the casing of the high pressure pump.